Well, a lot of reporting on the affiliate code situation partly mischaracterized what actually happened. There was an auto-complete suggestion that was auto-selecting when you pressed "enter", and it was fixed shortly thereafter. There is a blog post about it called "On Partner Referral Codes in Brave Suggested Sites".

That said, it does essentially the same thing Firefox does when you do a search on Firefox. Try right now: go into Firefox, type in a search in the URL bar, press enter, and you'll see it appends/"injects" a Firefox "affiliate code" as a query parameter so that Firefox gets a cut from Google. One salient difference is that Firefox's "affiliate code" is a vanity code (human readable: "?client=firefox-b-d"), so it isn't viscerally shocking.

If it read "?client=brave" like it does on Firefox, it's very likely no one would have ever cared!